Reverse Fin Cooling Fan Noise Reduction
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Solution Overview
Problem
Conventional cooling fans for small air-cooled internal combustion engines generate excessive noise due to air turbulence and blade pass frequency, which is not adequately addressed by existing designs.
Innovation Solution
The design incorporates a cooling fan with radially extending reversed fins that protrude further outward than the band, coupled with a screen having a hub and blades, to reduce turbulence and noise by optimizing air flow and blade pass frequency through specific fin geometry and spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional cooling fans are used, then cooling function is provided, but excessive noise is generated due to air turbulence and blade pass frequency
Solution Approach 1:
The patent applies inversion by reversing the conventional fin direction. Instead of fins extending forward from the rotation direction, the fins extend backward (reverse fins), which changes the air flow pattern and reduces turbulence-induced noise while maintaining cooling effectiveness. This inverted geometry fundamentally alters how air interacts with the rotating fins, solving the noise problem without sacrificing cooling performance.
Solution Approach 2:
The patent employs curvature by designing fins with specific arc angles and curved geometries rather than straight lines. The fins follow curved paths that optimize air flow attachment and reduce turbulence. This curved geometry allows the fins to guide air smoothly around the housing, minimizing chaotic flow patterns that generate noise while preserving efficient heat transfer.
2Object-affected harmful factors
If fin tips are positioned close to housing, then compact design is achieved, but air turbulence and noise increase
Solution Approach 1:
The patent applies local quality by creating different spacing relationships at different radial positions. The reverse fins are designed so that their tips maintain optimal clearance from the housing at specific locations, while the curved geometry allows varied spacing along the fin length. This localized optimization reduces turbulence at critical interfaces with the housing while maintaining overall compact dimensions.
Solution Approach 2:
The patent transitions from two-dimensional straight fin designs to three-dimensional curved fin geometries. By introducing arc angles and radial variations, the fins operate in multiple spatial dimensions, allowing them to navigate around the housing more effectively. This dimensional approach enables compact packaging while maintaining sufficient clearance to prevent excessive turbulence.
3Object-affected harmful factors
If standard fin geometry is used, then manufacturing is simplified, but noise from blade pass frequency is not reduced
Solution Approach 1:
The patent applies parameter changes by modifying key geometric parameters of the fins, including arc angle, radial length, thickness distribution, and spacing patterns. These parameter variations are optimized to change the blade pass frequency characteristics and reduce associated noise. By systematically adjusting these parameters, the design achieves noise reduction while maintaining manufacturability through controlled complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces noise by minimizing air turbulence and blade pass frequency, providing efficient cooling without excessive noise, as demonstrated by the increased spacing between fin tips and housing, and the co-rotation of the cooling fan and screen.
Implementation Method 1
The plurality of reversed fins extend radially outward from the rotational axis along a plurality of paths that are concave relative to a clockwise direction when viewed from above the cooling fan
Implementation Method 2
The design incorporates a cooling fan with radially extending reversed fins that protrude further outward than the band, coupled with a screen having a hub and blades, to reduce turbulence and noise by optimizing air flow and blade pass frequency through specific fin geometry and spacing
Implementation Method 3
The cooling fan is disposed at least partially within the internal space and is coupled to the shaft. The plate is positioned to rotate with the shaft about the rotational axis
Data Source
AI summary
An engine assembly includes a crankcase, a shaft, a housing, and a cooling fan. The shaft is coupled to the crankcase and defines a rotational axis. The housing has a sidewall that defines an internal space. The cooling fan is disposed at least partially within the internal space and is coupled to the shaft. The cooling fan includes a plate defining an upper surface and a lower surface. The plate is positioned to rotate with the shaft about the rotational axis. The cooling fan also includes a band that has an inner band radius and an outer band radius. The cooling fan also includes a plurality of reversed fins coupled to the band and extending from the upper surface of the plate, further radially outward from the rotational axis than the band.